1. Technical Field
The present invention relates to a system for cordlessly connecting an audio amplifier with a speaker using the radio, for example.
2. Related Art
Presently, there are commercialized multi-channel audio systems such as 5.1-channel surround systems. A multi-channel audio system makes it necessary to install speakers at four corner in a room so as to surround a listener. It is cumbersome to connect cables to the speakers from an audio amplifier. In addition, such cabling degrades the visual esthetic.
To solve this problem, there are proposed cordless speaker systems that cordlessly transmit audio signals as disclosed in Japanese Non-examined Patent Publication No. 2003-274499. The disclosed apparatus can control the speaker volume at the receiving side by superposing character multiplex data on an FM stereo signal.
However, the conventional apparatus uses an analog multiplexer to multiplex FM stereo signals. The configuration may become complex and costly. Presently, economically available transmission modules are limited to a type of two channels (or one channel). When an attempt is made to transmit and receive audio signals for three or more channels using one radio frequency, a special circuit configuration needs to be originally designed as mentioned above. There has been a problem of consuming a lot of time and costs.
Further, a front speaker and a center speaker are generally installed near the audio amplifier. Cable connection to an AV amplifier does not cause much trouble in cabling. It is expected to wirelessly transmit audio signals only to surround speakers and subwoofers.